Boris Bede converted on a 28 yard field goal for Montreal, but its offence struggled to find a rhythm and only managed four first downs after two quarters.
Brandon Bridge was one of four quarterbacks used by the Alouettes and orchestrated their best offensive surge in the third quarter.
Bridge completed a pass to Rainey to put the Als up 19-3. Bridge finished the game 4 for 8 and threw for 52 yards.
Jonathan Crompton also saw time behind centre for Montreal and struggled. He only completed 2-of-6 passes for 17 yards.
Stefan Logan — who had a good game — had a fourth-quarter fumble deep in the Alouettes zone. Ottawa got the ball on the 19 but Montreal's special teams blocked the kick.
Jonathan Hefney had an interception for the Als off Redblacks quarterback Henry Burris, which he returned from the 54 to the 6.
Khalil Paden had the lone touchdown for Ottawa.